P band Status

• Frequency Range:
  The P band receivers can be tuned in the frequency range 305-337 MHz with no more than a 15% variation in sensitivity.
  The tuning range can be extended to 303-342 MHz with as much as a 50% reduction in sensitivity near the edges of the band (see Table 4 ).
  
  
• Sensitivity and Elevation Effects:
  The system temperature of the P band receivers is generally in the range 150-180 K, depending on frequency and contribution from galactic sources. It can be as low as 130 K for observations at 330 MHz that avoid the galactic plane. The system temperature varies slowly with elevation at P band, mostly due to the increased path through the ionosphere with increased zenith distance; although the contribution of radio sources can cause significant variations (see figure). It is best to observe at elevations above 25 degrees in order to minimize ionospheric effects (mainly an increase in phase noise); although the large amount of flux detected in most P band observations generally allows phase correction through self-calibration.
  
  
  
• Interference (RFI):
  There are no frequency bands allocated to radio astronomy in the USA in the range of the P band receivers. The range of frequencies accessible to the VLA is allocated to mobile service use for military and aircraft communication. Strong external RFI is often present at 307.2 MHz, 317.7 MHz and 331.9 MHz. In addition, the electronics systems at the VLA generate some interference every 100 kHz, as well as stronger signals every 5 MHz and every 12.5 MHz (see VLA Test Memo #235 for details). A recent P band RFI plot is available at the VLA RFI page, which contains a detailed description of the RFI environment at the VLA.
  
  
  
• Recommended Defaults:
  P band observations should be done in Spectral mode with on-line Hanning-smoothing. The cleanest bands lie between 320-325 MHz and 325-330 MHz. RFI can be minimized using 3.125 MHz bands from 320-323.125 MHz and 325-328.125 MHz, which are the recommended defaults for observations in the D and C arrays. Higher sensitivity can be obtained with 6.25 MHz bands from 320-326.25 MHz and 325-331.25 MHz; although some RFI will appear in the data (generally in well defined channels that can be discarded if necessary) and there is some overlap between both bands (see VLA Test Memo #235 for details).